Could I be pregnant?

So i started taking birth control again about a month ago but stopped taking it all of a sudden because i ran out of pills. I started bleeding for a few days but it wasn’t my period it was because that’s what happens when you stop taking them. So a few weeks later, i had sex. (A little less than a week ago) we didn’t use protection and he nut in me. But this app said my period was to start that same day but it still hasn’t started and it’s been four days since then. But i also heard it’s hard to get pregnant right before your period. I’m 17.